c-erbB-2 (HER-2, neu) , a member of the epidermal growth factor gene family of ligands and receptors, is a protooncogene that encodes a 185 kD transmembrane glycoprotein (p185). This receptor has intrinsic tyrosine kinase activity and is involved in the pathogenesis of several adenocarcinomas including ovarian carcinoma. The biological consequence of the reduction of p185 in an inducible antisense cell line NIH: OVCAR-8 was a suppression of the anchorage-independent phentoype (Pegues, J. and Stromberg, K. Cancer Letters, 117, 73-79 (1997). Expression, phosphorylation and Heregulin-induced activation of all four erbB receptors were then examined as well as the effects of Heregulin (HRG) on the growth of five ovarian and three breast carcinoma cell lines. SK-OV3, NIH: OVCAR-3, NIH:OVCAR-8, Ovca 429 and Ovca 433 expressed all four receptors at variable levels by Western Blotting. However, erbB-3 was the only receptor that was constituitively phosphorylated (non-stimulated cells) in all five cell lines. These results are consistent with published data which demonstrate that the erbB-2/erbB-3 dimer is associated with the strongest signaling in the receptor homo- and heterodimeration heirarchy. Heregulin stimulation of these cell lines increased phosphorylation of only erbB-3 in NIH:OVCAR-8 and -3, and Ovca 429. SK-OV-3, the line which most highly over expresses erbB-2, and Ovca 433, which unlike the others is both non-clonogenic and non-tumorigenic, were unaffected. In receptor heterodimerization studies, erbB-3 and erbB-4 immunoprecipitation co-precipatated erbB-2 in all five lines. No ovarian carcinoma cell lines were growth-stimulated in monolayer or soft agar by HRG (up to 500ng/ml). However, HRG stimulated growth in monolayer and soft agar of all three breast lines examined. Hrg mRNA was not detectable in two of the three breast cancer cell lines examined. However, all five ovarian carcinoma lines expressed HRG mRNA by RT-PCR. These results, as suggested by the consistent expression of HRG mRNA and constituitve tyrosine phosphoylation of erbB-3 in all five ovarian lines, indicate endogenous production of HRG may account for their lack of a growth response to exogenous HRG. In constrast, exogenous HGR-induced proliferation in the breast lines SK-Br-3 and T47D may be due to their low or absent endogenous HRG production.